Estimation of the uncertainty of mass measurements from in-house calibrated analytical balances

The uncertainty evaluation of mass measurements when using “in-house” calibrated analytical balances is revisited according to the Guide to the expression of Uncertainty Measurement (GUM). The calibration of analytical balances is discussed according to the guidelines of several bodies such as ASTM, UKAS and DKD/PTB. The remainder components of uncertainty can be estimated from the balance data sheet specifications.     

平衡健身盐的开发及其疗效

平衡健身盐是根据平衡保健理论研制成功的新型老人保健餐桌盐，平衡健身盐的成分含有钾、钠、钙、镁、铁、锌、铜、硒、钴、碘、铬等几十种适合人体需要的天然元素，这些成分能够调节人体元素的平衡，许多医院临床结果指出：平衡健身盐有治疗心血管病人和高血压患者的确实功效，如：降低高血压(治愈率92％)，升高低血压(治愈率78％)，长期食用有助于治愈瘫痪病人等，建议每位老人每天食用8g平衡健身盐。     

当前光学塑料的研究方向及综合性能的均衡

根据结构与性能的关系对当前光学塑料的主要研究方向进行了归纳和总结，介绍了具有高折光指数、高耐热性及其它功能性的新型光学材料，指出了性能之间均衡对实现化的意义。     

微量元素与食物链研究的重点和方向

简要地综述了微量元素与食物链研究的重点、现状及取得的成果和存在的问题．并指出今后的研究方向．     

200W MCFC电池组的电化学性能及热平衡计算

MCFC电池组 (6对电池 ,电极面积 2 2 6cm2 )在 0 .9MPa/cm2 反应气压下 ,输出功率为2 17.6W .热平衡计算表明 ,该电池组在 30 0mA/cm2 电流密度下放电 ,当气体利用率为 2 0 %时 ,电池组处于热平衡状态下运行 .若维持此热平衡 (电池组内最高温度为 70 0℃ ,运行温度 6 5 0℃ )状态且提高反应气体利用率 ,则电池组热平衡点的电流密度将下降 ,以空气 +CO2 为氧化剂 ,H2 +CO2 为燃料气时 ,在不同气体利用率下电池组热平衡点的电流密度均大于 10 0mA/cm2 .提高电池组的输出功率 ,热电效率将下降 ;提高反应气压 ,热电效率相应提高     

Hidden Lives. Early Childhood Care as an Academic: The Slow Burn

As the inaugural entry in the new series Hidden Lives, this Viewpoint Article highlights challenges in early childhood care faced by academicians. Research centers must adapt to societal shifts in family structure, uncertainty around research funding, expanded job responsibilities and upheavals brought about by the pandemic. These problems represent opportunities for change at the technological, cultural and policy levels. It is crucial that we recognize those in need and help where we can.     

Shaping Tetraazaparacyclophanes for Selective Solvent Vapour Detection: Structural Variations in Coating Design

Paracyclophanes serve well as receptor sites mimicking enzyme analogue recognition. Their application as coatings for themass-sensitive detection of toxic organic solvent vapours is demonstrated involving synthetic variation of the macrocycle in terms of cavity size, shape and stereoelectronics. In this way it is possible to tailor these hosts towards different analytes such as chloroform or toluene. The computational modelling of the inclusion allows the prediction of both the sensitivities and selectivities of promising coatings before doing time consuming syntheses. Force-field calculations show that the outstanding inclusion behaviour of a xylylene bridged tetraazaparacyclophane towards large aromatic and halogenated analyte molecules is due to the elongated cavity of the host. Temperature-dependent determination of the equilibrium constant K of the guest inclusion shows that calculated and measured interaction enthalpies do correlate satisfactorily.     

基于质子条件式的终点误差精确式

容量分析中,滴定终点的误差决定了该分析方法的可靠性。根据质子条件式,可推导出终点误差的精确式。该表达式用滴定开始前而不是终点时物质的浓度进行计算;用滴定终点时的p H进行计算,不需要计算化学计量点时的p H;所得出的精确式具有通用性,能有效降低学习与记忆的难度,提高计算结果的准确度。     

CAHN－2000磁天平的调试与数据处理系统的研制

叙述了ＣＡＨＮ－２０００磁天平（美国）调试过程中如何解决液氮温区的测试，自制了磁天平与计算机的接口，编写了数据采集、处理和控制等高原 软件，节省了几万美元，部分指标超过原配套水平，三年来仪器在对国同外开放过程中，液氮温区的工作一直正常，实测了上千个样品，提供的数据已撰写数十篇文章在国内外刊物上发表。由此说明，要充分发挥进口仪器的使用效率，必须对仪器的工作原理、结构特点有透乇的了解，同时要有相当的自     

CAHN－2000磁天平的调试与数据处理系统的研制

叙述了ＣＡＨＮ－２０００磁天平（美国）调试过程中如何解决液氮温区的测试，自制了磁天平与计算机的接口，编写了数据采集、处理和控制等方面的软件，节省了几万美元，部分指标超过原配套水平。三年来仪器在对国内外开放过程中，液氮温区的工作一直正常，实测了上千个样品，提供的数据已撰写数十篇文章在国内外刊物上发表。由此说明，要充分发挥进口仪器的使用效率，必须对仪器的工作原理、结构特点有透彻的了解，同时要有相当的自制配套能力。     

Characterization of proteins by mass spectrometry. Invited lecture.

Plasma desorption and fast atom bombardment mass spectrometry have in the last decade demonstrated the potential of mass spectrometry for protein studies. The recently developed matrix-assisted laser desorption and electrospray mass spectrometry have expanded the analytical potential of mass spectrometry to cover nearly all proteins. The type of information obtained with the four methods is described and their performances are compared. The potential of combining mass spectrometric relative molecular mass information on proteins with the information contained in protein sequence databases is outlined and some typical fields of application of mass spectrometry in protein chemistry are described. The need for the full integration of mass spectrometry in the protein laboratory is discussed.     

Computational principles of determining and improving mass precision and accuracy for proteome measurements in an Orbitrap

Precision proteomics requires high-resolution and high mass accuracy peptide measurements. The Orbitrap instrument achieves excellent resolution on a chromatographic time scale and its design is favorable for very high mass accuracy. Here we describe how mass precision for each peptide increases successively by considering all associated measurements, starting from the MS peak and proceeding to its chromatographic elution profile, isotope envelope, and stable isotope pair in SILAC measurements. We extract peptide charge pairs to perform nonlinear recalibration of the Orbitrap mass scale through spline interpolation. The deviation of mass values determined from charge pairs is used to convert mass precision to mass accuracy for subsequent database search. The corrected mass precision is consistent with the mass accuracy independently determined by database identification. Individual mass deviations range from below 100 ppb for peptides with many associated mass measurements and good signal intensities to low ppm for peptides with few mass measurements and signals close to the noise level. This extremely high and individualized mass accuracy is equivalent to a substantial increase in database identification score.     

Balancing the Pauling bond orders in Kekuléan benzenoid hydrocarbons

We consider a cutting of the molecular graph B of a Kekuléan benzenoid molecule into two disconnected subgraphs, S and the other, by deleting from B certain edges. It is required that both subgraphs remain Kekuléan. The edges involved in this cutting are classified as starred and unstarred. A starred edge is incident to a starred carbon site of the subgraph S, whereas an unstarred edge to an unstarred carbon site of S. The following regularity is established: for any above-described cutting of any Kekuléan benzenoid system, the sum of the Pauling bond orders of the starred edges is equal to that for the unstarred edges.     

Applications of mass spectrometry in the trace element analysis of biological materials

The importance of mass spectrometry for the analysis of biological material is illustrated by reviewing the different mass spectrometric methods applied and describing some typical applications published recently. Though atomic absorption spectrometry is used in the majority of analyses of biological material, most mass spectrometric methods have been used to some extent for trace element determination in biomedical research. The relative importance of the different methods is estimated by reviewing recent research papers. It is striking that especially inductively coupled plasma mass spectrometry is increasingly being applied, partly because the method can be used on-line after chromatographic separation, in speciation studies. Mass spectrometric methods prove to offer unique possibilities in stable isotope tracer studies and for this purpose also experimentally demanding methods such as thermal ionization mass spectrometry and accelerator mass spectrometry are frequently used.     

Zooming-in on cancer metabolic rewiring with tissue specific constraint-based models

The metabolic rearrangements occurring in cancer cells can be effectively investigated with a Systems Biology approach supported by metabolic network modeling. We here present tissue-specific constraint-based core models for three different types of tumors (liver, breast and lung) that serve this purpose. The core models were extracted and manually curated from the corresponding genome-scale metabolic models in the Human Metabolic Atlas database with a focus on the pathways that are known to play a key role in cancer growth and proliferation. Along similar lines, we also reconstructed a core model from the original general human metabolic network to be used as a reference model.A comparative Flux Balance Analysis between the reference and the cancer models highlighted both a clear distinction between the two conditions and a heterogeneity within the three different cancer types in terms of metabolic flux distribution. These results emphasize the need for modeling approaches able to keep up with this tumoral heterogeneity in order to identify more suitable drug targets and develop effective treatments. According to this perspective, we identified key points able to reverse the tumoral phenotype toward the reference one or vice-versa.     

Flow injection of the lock mass standard for accurate mass measurement in electrospray ionization time-of-flight mass spectrometry coupled with liquid chromatography

A method of flow injection of the lock mass for accurate mass measurement using electrospray ionization time-of-flight mass spectrometry is described. The reference compound is introduced in the chromatographic effluent via a six-port valve placed post-column, prior to the split connector. Flow injection is performed in such a way that the reference elution peak is superimposed in the total ion current and partially overlaps that of the investigated analyte, allowing independent ionization of the two compounds and thus accurate mass measurement with no ion suppression effects. Different lock mass molecules can be injected in a single analytical run to target various analytes. The performance of this methodology is demonstrated in both isocratic and gradient liquid chromatography modes. The molecular ion of the flow-injected lock mass could also be used as a reference for mass measurement of the in-source fragments of the analytes. Good mass accuracy, within 4 mDa of the theoretical values, was obtained.     

Exact mass measurement of product ions for the structural confirmation and identification of unknown compounds using a quadrupole time-of-flight spectrometer: a simplified approach using combined tandem mass spectrometric functions

This article describes a simple method to perform lock mass corrected accurate mass measurements in tandem mass spectrometry (MS/MS) with a quadrupole time-of-flight (Q-TOF) mass spectrometer. The experimental approach consists of using the protonated molecule of a known compound, which is measured in a MS/MS function using low collision energy (no fragmentation), as mass calibrator. The unknown compound is acquired in MS/MS mode albeit using high collision energy. After the acquisition, the two MS/MS spectra of unknown and mass calibrator are combined, and the fragments of the unknown are lock mass corrected by using the protonated molecule of the mass calibrator. To prove this concept, 10 compounds were analyzed using this approach, the fragments interpreted and, where possible, related to structural data available in the literature. All the unequivocally assigned fragments were accurately mass measured with mass errors within appropriate limits, i.e. for m/z values <200 with a mass tolerance of 3 mDa while for m/z > 200 the mass tolerance is expressed as 10 ppm.     

Dependence of Performance of Organic Light-emitting Devices on Sheet Resistance of Indium-tin-oxide Anodes

IntroductionIndium-tin-oxide(ITO) has been widely used asthe anode material in organic light-emitting devices(OLEDs) because of its high transmittance in the visi-ble region and low electrical resistivity. In the pastyears, many investigations focused on …     

A collinear tandem time-of-flight mass spectrometer for infrared photodissociation spectroscopy of mass-selected ions

An apparatus based on collinear tandem time-of-flight mass spectrometer has been designed for the measurement of infrared photodissociation spectroscopy of mass-selected ions in the gas phase.The ions from a pulsed laser vaporization supersonic ion source are skimmed and mass separated by a Wiley-McLaren time-of-flight mass spectrometer.The ion of interest is mass selected,decelerated and dissociated by a tunable IR laser.The fragment and parent ions are reaccelerated and mass analyzed by the second time-of-flight mass spectrometer.A simple new assembly integrated with mass gate,deceleration and reacceleration ion optics was designed,which allows us to measure the infrared spectra of mass selected ions with high sensitivity and easy timing synchronization.     

Absolute quantitative electron microscopy of thin biological specimens by energy-dispersive x-ray microanalysis and densitometric mass determination

The method described is capable of measuring both the absolute mass and the mass fraction of elements is isolated thin biological specimens. To determine the elemental mass, characteristic x-rays emitted under electron irradiation are used, whereas the total mass of the specimen is found from electron scattering. Comparison with measurements on standards allows the calculation of the absolute elemental mass and elemental mass fraction values. The number of x-ray quanta per atom of a particular element, detected under strictly standardized procedural conditions, is given by a unit x-ray count value. Such values were determined for magnesium, phosphorus, sulfur and calcium using spray droplets as standard specimens.